1. Field of the Invention
The present invention relates a vibration apparatus for vibrating a dust prevention member disposed at the front of an optical device, such as an image pickup device provided in an image pickup apparatus and configured to obtain an image signal corresponding to irradiation light on its photoelectric conversion surface, or a display device provided in an imaging appliance, e.g., an image projection apparatus, and configured to display an image projected on the screen. The present invention further relates an imaging appliance, such as an image pickup apparatus or image projection apparatus, equipped with this vibration apparatus.
2. Description of the Related Art
In recent years, there are imaging appliances utilizing optical devices, such as an image pickup apparatus using an image pickup device or an image projection apparatus using a display device of, e.g., a liquid crystal type. The image quality of images generated by imaging appliances of this kind has been remarkably improved. Accordingly, in such imaging appliances, if dust is deposited on the image pickup device or display device, or an optical device disposed near the above-mentioned device, the dust casts a shadow on the generated image and brings about a serious problem.
For example, there is an image pickup apparatus designed such that a camera main body is equipped with a photographing optical system detachably attached thereto. According to this image pickup apparatus, users can optionally use desired photographing optical systems by attaching/detaching them to interchange them with each other, as needed. Digital cameras of the so-called lens interchangeable type are currently in practical use such that a plurality of different-type photographing optical systems are selectively used relative to a single camera main body, as described above. However, in the case of digital cameras of the lens interchangeable type, when a photographing optical system is detached from the camera main body, dust suspended in the surrounding environment of the camera may infiltrate into the camera main body. Alternatively, in these digital cameras, when various types of mechanical operation mechanisms, such as a shutter and aperture mechanism, built in the camera main body are operated, foreign particles may be generated therefrom and deposited as dust on the surface of the image pickup device.
Projectors for viewing magnified projection images are currently in practical use, wherein a light source and a projection optical system are employed such that images displayed on a display device of the CRT type or liquid crystal type are magnified and projected onto a screen. In the case of these projectors, dust may be deposited on the surface of the display device and cast a shadow on the screen in a magnified and projected state.
Under the circumstances, there have been developed various types of mechanisms to remove dust deposited on the surface of optical devices inside imaging appliances. For example, Jpn. Pat. Appln. KOKAI Publication No. 2004-64555 discloses an electronic image pickup apparatus equipped with a dust removing mechanism, which is designed such that a circular glass plate (dust prevention member) is provided with an annular plate-shaped piezoelectric device (vibration application member) fixed to its peripheral portion, and the piezoelectric device is supplied with a frequency voltage having a predetermined frequency to generate a standing wave bending vibration concentric with the center of the circular glass plate, thereby removing dust deposited on the circular glass plate. The vibration generated by the predetermined vibration application frequency is a standing wave having concentric nodes. A dust prevention member receiving member is disposed in contact with the dust prevention member concentrically with the concentric nodes of the standing wave to support the dust prevention member and to provide dust prevention between image pickup devices.
Jpn. Pat. Appln. KOKAI Publication No. 2011-234055 discloses that a rectangular plate-shaped dust prevention member is provided with a strip shape piezoelectric device along its one side, and the piezoelectric device is configured to generate a vibration having a predetermined frequency to cause the dust prevention member to resonate, so that a standing wave is formed in a resonance vibration mode that generates a vibration concentric with the center of the dust prevention member. This publication further discloses the following matters: A plurality of standing wave vibration modes are generated by causing resonance with different frequencies to change the positions of vibration nodes so as to remove dust deposited at the vibration nodes of each vibration mode. Standing waves having different frequencies are generated to be substantially coincident with each other at a vibration node and the dust prevention member is supported by a support member at a position near the vibration node to reduce vibration loss. A frame-shaped seal having a lip shape in cross section is disposed between the image pickup face side and the dust prevention member to prevent dust from infiltrating.
Jpn. Pat. Appln. KOKAI Publication No. 2012-153023 discloses that a layered film having a high piezoelectric property (with a large piezoelectric “d” constant) can be formed by layered poly-L-lactic acid or poly-D-lactic acid layers and stretching them in a predetermined direction.